"1_ Lewis Dot Diagrams"
Lewis Dot Diagrams Try Nitrogen and Gallium 1) Lewis Dot Diagrams another way to show electron configuration G. N. Lewis also allows us to visually represent 1875 - 1946 bonds and molecule shape named after G.N. Lewis 1) Lewis Dot Diagrams diagram creation Cl write the atomic symbol imagine 4 orbitals around the symbol each orbital can hold 2 e- (max) put dots in, to represent valence e- put one electron In each orbital before doubling up # dots = # valence electrons 1) Lewis Dot Diagrams Electrons are divided between core and valence electrons for Lewis Dot Diagrams: valence e- are only those in the highest principle quantum number B - 1s2 2s2 2p1 valence = 2s2 2p1 Br [Ar] 4s2 3d104p5 Br valence = 4s2 4p5 this way Lewis Dot Diagrams will normally have 8 e- (ie, dots) max 1) Lewis Dot Diagrams recall: Atoms like to either empty or fill their outermost level. Since the outer level contains two s electrons and six p electrons (d & f are always in lower levels), the optimum number of electrons is eight. This is called the octet rule. 1) Lewis Dot Diagrams examples O O O H He Ne 1) Lewis Dot Diagrams vocab: a lone pair of e- or just “lone pair” O bonding electrons note: all of the dots are valence e- so…oxygen has 2 lone pairs and 2 bonding electrons (6 valence e-) 2) So What? drawing atoms in this way helps us understand covalent bonds recall: covalent bonds - sharing of e- ionic bonds - transfer of e- these diagrams are not as useful with ionic bonds ions in ionic bonds already have full octets Lewis diagrams would be pretty boring 2) So What? we call them “bonding electrons” for a reason Cl needs 1 more e- consider: H Cl H needs 1 more e- how many e- does H need to be “happy”? what about Cl? these two “unhappy” atoms can work together to both be “happy” by SHARING their bonding e-! 2) So What? H Cl electrons in different “unhappy” atoms will rearrange themselves, and form bonds to become “happy”! H Cl H is happy Cl is happy it has 2 e- it has 8 e- notation note: to show where the e- originally came from, we often use x’s and o’s to distinguish between electron origin H Cl = H Cl x we also show the e- between atoms (the bonding e- ) as a line H- Cl shared or bond pair e- This is the the LEWIS STRUCTURE of HCl. 3) Steps to Build a Lewis Structure 1. Draw the lewis stucture of the central atom (normally the “single” atom) N 1 Ns in NH3 3 Hs in NH3 N is the central atom 3) Steps to Build a Lewis Structure 2. Draw the other atoms around the central one H x N H x H x 2. Start pairing up the electrons (using circles or lines) 3) Steps to Build a Lewis Structure 4. Carefully redraw the bond pairs as lines. H x N H x H x 5. If needed, move electrons around to keep octets (more on this later) NOTE: H N H x x x H a bond is just a pair of electrons NH3 has 3 bond pairs and 1 lone pair of e- notice: each atom is now “happy” each H has 2 e- and the N has 8 e- Try It! Draw the Lewis dot structure for: H2O be sure to follow the steps! CH4 Homework page 244: #1-5 read page 243 - 246 Draw the Lewis Structure for: H2O2 each atom has an octect CO2